There are many innocents in the epic battle between good and evil. Some people will join on the side of good because the evil invaders destroyed their home. A lot of people will join on the side of evil because Evil Is Sexy, Rule of Cool, or just 'cause.
Then there are the people who deliberately try to stay out of the conflict. These could be the people in the Hidden Elf Village or the Actual Pacifist. Often they don't have a dog in the fight either way or they're just opportunists supporting both sides. No matter how you slice it, these people don't support either side more or less than any other side. That is, until the good guys turn out to be a bunch of self righteous jerkasses or the villains Kick the Dog. At that point, it's on and there's going to be hell to pay.
This Trope comes in two varieties.
The first kind is rather straight up. The neutral party is initially undecided until the villains decide to desecrate the Crystal Dragon Jesus. Then the neutral party will oppose the villains from then on.
The second kind is less frequently used. As it turns out sometimes heroes and villains are really bad at making first impressions. After initially meeting the heroes the neutral party will decide that evil is so much cooler and join them, or vice versa. This isn't a Heel-Face Turn or a Face-Heel Turn because these people were neutral at the start of the story and would have remained so if the villains and/or heroes weren't a bunch of a-holes. They will often only go out of their way to oppose someone out of vengeance.
The island nation of Orb in Gundam SEED is vehemently neutral: one of their central beliefs is complete non-involvement in any wars that have nothing to do with them. In order to protect their neutrality, however, they have developed some of the most advanced military technology in the world. So the Atlantic Federation attacks them to gain it... and succeeds, except that Orb proceeds to destroy their own infrastructure rather than let the Federation have it. The remaining Orb forces throw in with the Three Ships Alliance, which opposes both sides of the war and plays a major role in ending the conflict.
In Gundam Seed Destiny, shortly after the start of the series, Orb throws their lot in with the Earth Forces in order to avoid getting attacked and destroyed again. The characters involved with the Terminal (a secret underground organization that grew from the Three Ships Alliance) spend the duration of the series trying to invert this trope, with mixed results.
Spider-Man had his Neutral No Longer moment in his origin story after his refusal to stop a thief on the grounds that it wasn't his problem got his Uncle Ben killed. He gave up on using his powers for fame and fortune and became a superhero.
It takes nearly the entire series for Cade Skywalker to stop being a selfish Jerkass. After the Sith have endangered and killed just about everyone he gives a damn about, Cade declares war on them though he still doesn't accept the Jedi calling yet. That doesn't happen until the Final Battle.
Not really. While Cade doesn't sign on with the Imperials or Jedi, he is pretty consistently against the Sith.
Doctor Strange started out as a Dr. Jerk who cared only about himself. When circumstances confined him to the hidden retreat of the Ancient One, he realized very quickly that magic is real — and that it can be used for evil. Though he had come to the Ancient One to heal his hands, he changed his request and asked to learn magic instead, so he could fight back.
Uatu The Watcher is a prime example. His race of omniscient watchers swears an oath of neutrality. But as Galactus approached Earth, intent on consuming it, Uatu spoke directly to the Fantastic Four, telling where to find the Ultimate Nullifier. Not a direct alignment change, but enough involvement to end his neutrality.
Rick Blaine, and eventually Captain Renault, in Casablanca.
Not entirely, as he did express his hatred for the Empire from the very beginning and wanted to join the Rebellion as many of his friends had done. Obligation toward his family kept him on Tattooine. Han Solo better fits the trope, as his only interest in assisting the Rebellion at first was to get up enough money to pay off Jabba the Hutt. Attachment to Luke and especially Leia, seeing what the Empire was up to first-hand, Chewbacca talking him into it, and Darth Vader freezing him in carbonite and shipping him to Jabba probably sealed the deal. Given that Chewbacca was Good All Along, having assisted the Old Republic and the Jedi as a high-level decision-maker in Revenge of the Sith, it's possible Chewie exercised a Batman-Gambit to enlist the galaxy's best smuggler into the Rebellion.
Lando Calrissian is also an example. All he wanted was for the Empire to leave him alone to run Cloud City in peace, and was willing to sell out his old friend Han to get that. When Vader broke the deal they had made, though, Lando joined the Rebellion, this time for good.
Serenity has "I aim to misbehave": Mal, who pretty much just wants to be left alone and fly under the Alliance's radar (after losing a war against them and having a Heroic BSOD), finally decides to act against the Alliance by getting the word out about the atrocities they committed in search of a perfect world.
In the book, not as much. The Ents hold Entmoot, and decide to attack Saruman. In the movie, though, they initially decide to remain neutral, and only change their minds when Tree beard comes across a field of felled trees. Either way, the outcome is an awesome Curb-Stomp Battle.
Night by Holocaust survivor Elie Wiesel pleads the readers to turn to this trope.
The smugglers of the Star Wars 'verse are typically neutral - they'll take any job you happen to want, regardless of faction, and then take your competitors' tomorrow.. until the Empire starts encroaching just a little on their line of work. First they take Talon Karrde prisoner to keep him from revealing (i.e. selling) the location of the Katana fleet. After he gets broken out of prison, Karrde promptly turns around and gives it to the New Republic. Then the Empire hires a mole to stop the smugglers from banding together, who promptly ordered a hit on a smuggler meeting that killed the one unarmed guy in the room and approximately no one else. Turns out upsetting an entire underworld's worth of cutthroat low-lives is a bad idea.
Then the Yuuzhan Vong go and make exactly the same mistake by breaking a mercenary contract. With the Mandalorians. Yeah, that'll work.
In the Old Kingdom series, there were nine superpowerful magical beings in The Beginning. When the most powerful of them, The Destroyer, wanted to destroy the world again, seven of the others allied and bound him. The eighth one, Yrael, decided to remain neutral. But when The Destroyer gets free, Yrael unexpectedly decides to help bind him again.
He does more in the book than in the miniseries. In the latter, all he does is kill his wife's lover, although, by Fremen custom, he should've challenged him to a duel first. Stilgar, who has promised neutrality, kills him in retaliation. In the book, this is not enough. Duncan proceeds to taunt and insult Stilgar until the latter is furious. Only later does Stilgar realize that this was what Duncan wanted all along. The book also specifies that Alia took the guy as a lover only because she knew he was a traitor and wanted to flush out the conspiracy.
In the Honor Harrington books, this is played straight by the Andermani Empire. At one point the Andermani and the Manticorans come dangerously close to going to war, with ships firing on each other, but the revelation of Havenite operations in the area (including False Flag Operations and a major attack on the Manticoran base at Sidemore Station) push the Andermani the other way. And of course, let's not forget the Solarian League.
In The Dresden Files, the Faerie Courts of Winter and Summer are neutral to the war between the White Council of Wizards and the Red Court of vampires. They offered the Council access through their territory (letting the wizards take advantage of the Alien Geometries of Faerie) but were otherwise neutral. Then in Dead Beat, the Red Court invaded Faerie in an effort to wipe out the senior leadership of the Council after an already-devastating victory, and Summer immediately fell all over the Reds, with Summer declaring war on the Red Court for the transgression. However, the Summer forces could not go on the offensive because Winter refused to move against the vampires and made to threaten Summer's borders, which only allowed the Summer fae to provide limited support to the wizards.
In the Dragaera universe, a rival Dragonlord attempts to start a war with Morrolan, who employs Vlad as a security consultant. Vlad makes no effort to support Morrolan until Fornia's men come to his house and threaten him to make sure he stays out of it. Now that they've threatened him, and, further, have broken a rule he and the rest of the underground criminal syndicate hold sacred, he ispissed,joins Morralan's army out of pure spite, and winds up being a central figure in the final battle of the war.
Live Action TV
Star Trek: Deep Space Nine: The Romulans insisted on remaining neutral in the war between the Dominion and the Federation/Klingon alliance. The Federation was taking such heavy casualties that Starfleet realised they could not win the war without gaining allies. The only race powerful enough to make a difference was the Romulan Empire, who had no reason at all to drop their neutral stance due to the fact their three major rival powers were exhausting themselves while they watched from the sidelines in the hope they could mop up the Alpha Quadrant after the war was over. Sisko decided to do something to bring the Romulans into the war on the Federation's side and recruited Garak to come up with the franchise's best example of a Batman-Gambit to achieve it.
In a Star Trek Expanded Universe novel, the entire plot is revealed to have been a ploy by Starfleet Intelligence to bring the Klingons out of their neutral state in regards to Federation-Romulan negotiations on the side of the Federation by making the Romulans appear to be dishonorable and underhanded (not a difficult task, mind you). This results in the Treaty of Algeron, when the Romulans close their borders for several decades in exchange for the Federation banning all cloaking research.
Combination of the two types: on the one hand, he has bonded with planet earth and its denizens, i.e. the good guys in this story, and wouldn't be doing this otherwise. On the other, it wasn't enough to make him take sides until Lucifer went and started slaughtering his friends and girlfriend at the pagan god convention, so if Luci hadn't Kicked The Dog, he mightn't have had to face Gabriel.
Mind, all he winds up doing is buying a few minutes. Awesomely.
Gabriel: Lucifer, you're my brother, and I love you. But you are a great big bag of dicks.
Oh, except he also winds up telling the brothers how to stop Lucifer for good.
On the Community episode "Pillows and Blankets", while a campus-wide Civil War ragea round him, Jeff first exploits the conflict for personal gain. However, he makes a genuine stance once he sees that the friendship between Troy and Abed has seriously deteriorated. (Subverted in that instead of picking a side to support, he works towards the pair's reconciliation.)
In the earliest episodes of Doctor Who the Doctor was nowhere close to the altruistic hero he is now. He traveled mostly to satisfy his own curiosities. It wasn't until his seventh serial, "The Sensorites", that he did the right thing precisely because it was the right thing to do.
The third act of Dragon Age II revolves around Hawke finding it increasingly difficult to remain neutral as the tensions between the Mages and Templars rise in Kirkwall. At the end of the game, Anders destroys the Chantry, leaving there no middle ground left and no way to resolve the situation peacefully, forcing Hawke to pick a side.
Another one from BioWare and Star Wars: Jolee Bindo from Knights of the Old Republic is a ex-Jedi in Sour Armor who left the Order and had self-exiled himself. Despite being neutral on the Karma Meter, and making a good show of not caring about the outcome of the current war, he is very quick to scold a player's Dark Side acts. When it comes down to the wire, he chooses the path of a Jedi and will positively refuse to join you if you choose Dark Side.
Fallout: New Vegas has four endings to the main quest, three of which involve siding with one of three factions (the New California Republic, Caesar's Legion, or Mister House, with the fourth option to be seizing power for him/herself). In order to move into Act III of the game, the player must invoke this trope, forsaking at least two of the factions. There are even a handful of quests, such as "The House Has Gone Bust!" that can't be completed, only failed; the notification that you have failed them is letting you know that you have reached this stage.
In Mega Man Zero 4, the human refugees of Area Zero, known as Caravan, prefer to stay out of the war between the La Résistance (who they only see as terrorists with petty goals) and Neo Arcadia (which has fallen into dictatorial rule). However, over the course of the game, upon seeing that the Resistance's goals were no different from their own, the Caravan finally welcomes their help in fighting off and finally defeating the Neo Arcadian army. At the end of the game, in fact, they all mourn forZero's Heroic Sacrifice, knowing that all of it would never have been possible without his efforts.
And in Suikoden V, one of the Stars is a doctor who struggles to remain neutral in the civil war due to a desire to help the wounded and ill on both sides. Eventually, however, he begins to realize that the Godwin's absolutely have to be stopped, and promptly joins the Prince's army.
Suikoden V also has the Oboro Detective Agency, who go through several layers of this. First, Oboro must be convinced to officially join the Prince, which can go very easily if he was impressed by the Prince helping out their investigation earlier or poorly if the Prince made a wrong choice or two (or missed out on the investigation entirely). When he finally does join, Sagiri chooses to Opt Out, staying with the agency but refusing to join the war effort... unless the Prince finds somebody else and tries to recruit them, leading to Sagiri revealing her reasons for not wanting to fight before deciding to sign on anyway.
Played with in the second Avernum game: the Empire-Avernum War is interrupted by the Vahnatai, who start out as "neutral" in the sense that they're targeting all humans due to the theft of their revered Crystal Souls. When Imperial involvement in the theft is exposed - and, more importantly, when your party clears the Avernites of any wrong-doing - the Vahnatai side with your people against the Empire.
Subverted in the third and fourth games, when Rentar-Ihrno continues to seek vengeance against first the Empire and then Avernum, despite the majority of the Vahnatai preferring to remain neutral.
In World of Warcraft: Cataclysm, the new playable races, the worgen on the Alliance side, and the goblins on the Horde side, are suddenly thrust into the conflict by the re-emergence of the black dragon Deathwing, and the subsequent run-ins with opposing factions. The worgen, whose isolationism is forcibly broken by the Cataclysm, are fighting off an invasion by the undead Forsaken who want to annex their lands for a strategic harbour. The goblins escape a volcanic eruption on their home island, only to be shipwrecked after their boat is sunk by Alliance crossfire at sea.
The High Elves originally wanted to stay out of the various wars, and only aided the Alliance enough to defeat the Horde during the Second War. While some remained part of the Alliance, the majority retreated to their nation and tried to ignore the Third War... until the Scourge invaded and killed ninety percent of their population. The survivors tried to make amends with the Alliance, but their liaison took every opportunity to try and undermine them, eventually leading to their racial Face-Heel Turn.
The novel Wolfheart shows that the process of the worgen becoming part of the Alliance is far from smooth. Namely, most of the Alliance members approved... except for King Varian Wrynn of Stormwind, the strongest member of the Alliance. Varian isn't so much opposed to the animalistic nature of the worgen as to the fact that they left the Alliance when the Alliance needed them. Later on, Varian and King Greymane reconcile their differences, and Varian leads the worgen in a charge the utterly devastates the Horde, which is in the process of curb-stomping the night elves.
In the forthcoming Mists of Pandaria expansion, Jaina Proudmoore goes down this path after her home base, Theramore Isle, gets attacked and destroyed by Horde Warchief Garrosh Hellscream's forces. And by proxy, Garrosh has also declared war on the avowedly neutral Kirin Tor and blue dragonflight.
Similarly, in Mists, the so-far totally neutral Klaxxi Paragons, and perhaps their entire race, join Garrosh and the (evil) Horde. They are bosses in the Siege of Orgrimmar raid. This is solely because Garrosh possesses the heart of their deity, which they said they outright stated at the beginning that they would turn on you for. No one probably would have guessed that the Klaxxi would join GARROSH of all people, but at the moment, he IS their god incarnate, therefore, they have finally chosen a side. This cannot end well for them.
In Final Fantasy VI the city of Narshe originally refused to take a stand against the Empire, believing it only attacked people who sided with the Returners. After the Empire attack them a couple of times anyway, to get at the Frozen Esper, they decided to join with the Returners.
Cloud of Final Fantasy VII starts off neutral towards Shinra, though he gets personally invested in the conflict eventually.
In the early timeline of the X-Universe the Boron are relatively small and weak and just want to be left alone. The Argon are emphatically not small and weak, but they too have chosen to remain neutral. The Split, a trigger-happy race of violent psychopaths, hate the Boron and start a war with them. The poor militarily-inferior Boron are reduced to just their home sector, and this slaughter finally moves the Argon to pity. They renounce their neutrality, turn on their war machine on the Split and curb-stomp them back to their home sectors. A long alliance with the Boron results.
The Boron, having almost been annihilated, finally understand that neutrality is impossible, and they themselves gear up for war.
In The Elder Scrolls V: Skyrim, Jarl Balgruuf the Greater of Whiterun initially maintains a position of neutrality in the Civil War, refusing to get involved (though he has no fondness for Ulfric Stormcloak). Eventually, if you start the questline, Ulfric forces his hand by sieging the city of Whiterun, causing Balgruuf to side with the Imperials. Speaking to him afterwards will have him reveal that he has nothing but contempt for Ulfric, who he regards as a power-hungry barbarian.
In an online game called Memesville 2, one of the neutrals (who just had to survive to win) was trying to help those who were being lynched if they were neutrals like him. Then one Villain, who could changed who she appeared as, lied to him to try and live, but failed. Then they killed the one guy he KNEW was a Neutral. His response? "... ... ... Alright, villains. Thanks for choosing my side for me."
In Worm, Parian, who previously used her powers (mental control of objects like thread and cloth) as an advertising gimmick for her fashion career, is forced into this position in order to get enough money to pay for medical treatment for her friends and family-specifically, she joins the local supervillain gang that is taking over the city, much to the horror of her superhero friend Flechette.
Happened with the Constructicons in the Transformers Animated cartoon. Initially they were neutral hedonists and were even friendly to Bulkhead, but after Optimus Prime was a bit of a Jerk Ass to them they threw in their lot with the far more seemingly benevolent (and generous with his oil) Megatron.
Tigertron does this in Beast Wars. He wakes up from stasis all confused, not certain who he is, when he sees the Predacons threaten to kill an innocent animal if the Maximals don't surrender their friend. The Maximals surrender — and he realizes who the good guys are.
The Flutter Ponies in My Little Pony The Movie are the only creatures which can drive off the overwhelming purple glop known as Smooze, but they insist it's "not their fight." It takes a Rousing Speech by the Ponies' human ally, Meagan, to convince them to help.
That and Lickity Split and her friends saved one of their own.
Played with in an episode of Road Rovers, the president of Switzerland, under hypnotic suggestion, almost launched a missile strike against the other nations. After coming out of it, he immediately declares "We are neutral again!"
Apparently, in some places, watching traffic from the curb is a national spectator sport. The Stryker ICV is a favorite with the youngest fans. One day somewhere in Baghdad, a convoy was moving one of these. Simultaneously, a group of insurgents moving an IED entered the same intersection. The insurgents panicked and triggered the device. Locals were appalled at the lack of concern for civilian life and began cooperating with the NATO forces.
This serves as an allegory for pretty much the entirety of the occupation. The insurgents have had much, much less concern for innocent life, detonating devices in near schools, restaurants, and other public places. This has led to a lot of the civilians siding with the occupation forces.
Really, this trope has pretty much been America's Hat. Examples:
The U.S. sat out the Cuban rebellion against Spain for about fifteen years until the USS Maine blew up in Havana Harbor, which got the U.S. into the war against Spain.
The U.S. stayed neutral in World War One until it looked like German victory was imminent and the Germans were caught attempting to form an offensive alliance with Mexico against the United States.
The U.S. didn't really start to help the Allies in World War II until after the fall of France, and did not get into the war until after Pearl Harbor, and did not declare war against Germany until after Germany declared war against the U.S.
When the Cold War began, the Truman administration was quite indifferent to what happened in mainland east Asia, cutting off aid to Chiang Kai-shek and the KMT in the critical year of 1946, and then, after the Communists took over China, withdrawing American forces from Korea and declaring South Korea to be outside the American "defense perimeter in Asia." When the North Koreans then promptly invaded South Korea with Soviet and Chinese backing, the U.S. intervened on the South Korean side.
When Lyndon Johnson became President, he declared that he was "not going to send American boys halfway around the world to do a job that Asian boys can and should do for themselves." When it became apparent in 1965 that South Vietnam was months if not weeks from falling to the Communists, however, and Communist forces fired on a U.S. naval vessel in the Gulf of Tonkin, he did exactly that.
Contrary to popular belief, the U.S. was largely neutral in the Arab-Israeli conflict until the early 1970s, and did not, for example, intervene to open the Strait of Tiran in 1967 despite an earlier promise to do so. But when during the Yom Kippur War of 1973, the Soviet Union sent a massive airlift of supplies to the Egyptians and the Syrians, and the Israelis announced that they were seriously considering going nuclear in response, the Nixon administration decided to send an American airlift of supplies to Israel. This is only a partial example, however, since the United States only sent supplies, and did not intervene directly.
In 1990, American ambassador April Glaspie met with then-ruler of Iraq Saddam Hussein to ask him about the troops he was massing on his border with Kuwait and the threats he was making toward Kuwait. He apparently assured her that he was just saber-rattling to win diplomatic concessions on a border dispute, and she seems to have understood him to say that he was committed to resolving the dispute peacefully. She famously assured him, however, that the U.S. has "no opinion on your Arab-Arab conflicts, such as your dispute with Kuwait....the Kuwait issue is not associated with America," and he may have taken that as a green light to invade Kuwait. Suffice it to say that when he did, the U.S. sent troops to the Persian Gulf, first to defend Saudi Arabia, but then to liberate Kuwait.
Later in that decade, during the Balkan wars that followed the break-up of Yugoslavia, the United States did not intervene for several years in the war in Bosnia, but did finally decide to back Croat intervention on the side of the Bosniaks against the Serbs, after watching Serb attacks on Sarajevo and other Bosnian towns on the news every night for years. Then, when the Serbs went to war in Kosovo to attempt to prevent that province from breaking away, the U.S. decided to intervene directly, launching an air campaign against Serbia.
Also during the 1990s, the United States was neutral in the civil war in Afghanistan between the Taliban and the Northern Alliance, even as the Taliban took over most of the country, pushing the Northern Alliance into a tiny strip of territory in the north. After September 11, 2001, however, the United States intervened in Afghanistan on the side of the Northern Alliance, and removed the Taliban from power; the "civil war"/insurgency continues to this day, however.
So, yeah, this trope could easily be given the alternate title of "American Foreign Policy." It's a double-edged sword though; sometimes America takes flak for trying to stay out of other people's conflicts ("How can you stand aside and watch this happen?!"), while at other times it is criticized for trying to play policeman to the world ("What gives you the right to interfere in other countries?!"). Historically speaking, American foreign policy gave up on actually being neutral in international affairs after WWII, when isolationism among the various world powers gave Nazi Germany a head start on world conquest because nobody wanted to get involved when they started rolling over small neighbor countries.
Italy in both World Wars. In World War I, Italy was supposed to immediately enter the war on the side of Germany and Austria-Hungary, but refused due a loophole and stayed neutral for about a year before entering the war AGAINST them. In World War II it happened TWICE: first Italy was supposed to join Germany as soon as France and Britain declared war, but stayed neutral until the war appeared to be already won and attacked France and a small British colony just for the show, only to get held off by the French and find out the hard way that the British Empire wouldn't surrender; in 1943 an invaded Italy sued for peace and became neutral again until the German reinforcements sent to help the defense were ordered to become an occupation force.
Vichy France was a subversion during World War II. The government (including France's colonies) was neutral in the war (at least officially). In particular they were guaranteed control of the French Navy, which they promised to the Allies they would not allow to fall into German hands. Evidently lacking confidence in this promise (or the Vichies' ability to keep it), the Royal Navy seized several French ships and fired on the French fleet at Mers-el-Kébir. There were numerous skirmishes between Vichy French and Allied forces after this, and Vichy neutrality effectively ended with Case Anton, the German seizure and occupation of all of Vichy France. As it turns out, the French kept their promise regarding their Navy, scuttling their ships in the harbor at Toulon.
To protest against SOPA and Protect IP, Wikipedia blacked out their website on January 18, 2012. Wikipedia is notable for staying as True Neutral as possible, making this a huge change in their policy. Ironically enough, they had to break their own neutrality in order to fight for the principle of neutrality.